Watermarking method with print-scan compensation

ABSTRACT

A digital watermark may be applied to digital image data to produce watermarked digital image data. A transformation may be applied to the watermarked digital image data to produce transformed watermarked digital image data. The transformation may approximate the inverse of a transformation that represents distortion caused by transmission through a print-scan channel.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned copending patent application Ser.No. ______ Attorney Docket No. F-713 filed herewith entitled “FragileWatermark for Detecting Printed Image Copies in the names of BertrandHaas, Robert A. Cordery and Claude Zeller; and Ser. No. ______ AttorneyDocket No. F-714 filed herewith entitled “Detecting Printed Image CopiesUsing Phase-Space-Encoded Fragile Watermark” in the names of Robert A.Cordery, Claude Zeller and Bertrand Haas.

BACKGROUND

This invention relates generally to the field of printed documentsecurity, and more particularly to image data processing for the purposeof watermarking printed images.

It has been proposed to include watermark data in digital image data sothat resulting printed images contain watermarks. The purpose of thewatermarks may be to authenticate the printed images. That is, forexample, fragile watermarks may be placed in original images to allowcopies to be distinguished from originals; or robust watermarks may beplaced in original images to allow the source of first or latergeneration copies to be ascertained. However, the process of printing animage and then scanning the printed image to retrieve the watermarkresults in scanned image data that is distorted relative to the originalimage data used in generating the printed image. This distortion in the“channel” by which the scanned image data is obtained from the originalimage data may compromise detection or other processing applied to thewatermark in the scanned image data.

SUMMARY

Accordingly, methods are provided for transforming data used to printimages so as to improve the quality of the watermark in the printedimage.

In one aspect, a method includes providing digital image data thatrepresents an image. A digital watermark is applied to the digital imagedata to produce watermarked digital image data. A transformation isapplied to the watermarked digital image data to produce transformedwatermarked digital image data. The transformation is at leastapproximately an inverse of a print-scan distortion transformation. Asused herein and in the appended claims, a “print-scan distortiontransformation” refers to a mapping or other operation that digitallyapproximates the effect (other than random noise) on first image data ofprinting an image with the first image data and then scanning theresulting printed image to produce second image data.

The print-scan distortion transformation may be applied to the digitalimage data prior to the step of applying the digital watermark to thedigital image data.

An image may be printed on the basis of the transformed watermarkeddigital image data and the printed image may be scanned to producescanned image data. The scanned image data may be analyzed to retrievethe watermark in the scanned image data. The printing of the image maybe performed by a postage meter in which the transformed watermarkeddigital image data has been loaded.

In another aspect, a method includes providing watermark data thatrepresents a digital watermark and applying a transformation to thewatermark data to produce transformed watermark data. The transformationis at least approximately an inverse of a print-scan distortiontransformation. The method further includes providing digital image datathat represents an image and combining the transformed watermark datawith the digital image data to produce watermarked digital image data.

An image may be printed on the basis of the watermarked digital imagedata and the printed image may be scanned to produce scanned image data.The scanned image data may be analyzed to retrieve the watermark in thescanned image data. The printing of the image may be performed by apostage meter in which the watermarked digital image data has beenloaded.

By inverse-transforming watermark data, or inverse-transforming imagedata that has been watermarked, the watermark may, in effect, passthrough the print-scan channel with reduced distortion, which maypromote improved detection or facilitate other processing of thewatermark.

In still another aspect, a method includes providing image data thatrepresents an image and applying a digital watermark to the digitalimage data to produce watermarked digital image data. A print-scandistortion transformation is applied to the watermarked digital imagedata to produce transformed watermarked digital image data. Acharacteristic of the watermark as represented by the transformedwatermarked digital image data is retrieved. The method further includesprinting an image on the basis of the watermarked digital image data andscanning the printed image to produce scanned image data. Acharacteristic of the watermark as represented by the scanned image datais retrieved. A comparison is made of the watermark characteristics asthe watermark is respectively represented by the transformed watermarkeddigital image data and by the scanned image data.

Therefore, it should now be apparent that the invention substantiallyachieves all the above aspects and advantages. Additional aspects andadvantages of the invention will be set forth in the description thatfollows, and in part will be obvious from the description, or may belearned by practice of the invention. Various features and embodimentsare further described in the following figures, description and claims.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description given below, serve to explain the principles ofthe invention. As shown throughout the drawings, like reference numeralsdesignate like or corresponding parts.

FIG. 1 is a block diagram that illustrates an apparatus provided inaccordance with the invention for printing a watermarked image as partof a postage indicia.

FIG. 2 is a flow chart that illustrates a process that may be providedin accordance with the invention for generating and printing watermarkedimages.

FIG. 3 is a graph that illustrates a transformation that may be appliedto pixel values of an image to simulate changes in pixel values that mayresult from printing an image using the pixel values and then scanningthe printed image.

FIG. 4 is a graph that illustrates a transformation that issubstantially the inverse of the transformation illustrated in FIG. 3.

FIG. 5 is a flow chart that illustrates a process that may be providedin accordance with an alternative embodiment of the invention forgenerating and printing watermarked images.

FIG. 6 is a block diagram of an apparatus that may be provided inaccordance with the invention to examine printed images.

FIG. 7 is a flow chart that illustrates a process that may be providedin accordance with the invention to retrieve a watermark in a printedimage.

FIG. 8 is a flow chart that illustrates a process that may be providedin accordance with another alternative embodiment of the invention.

DETAILED DESCRIPTION

In the method of the present invention, a transformation that issubstantially or approximately the inverse of a print-scan distortiontransformation is applied to watermarked image data, or to watermarkdata prior to combining the watermark data with image data. Thetransformation applied to the watermarked image data or to the watermarkdata pre-compensates for distortion that will occur in the watermarkduring printing followed by scanning of the printed image. Detection orother processing of the watermark from the scanned image data isimproved.

Referring now to the drawings, and particularly to FIG. 1, the referencenumeral 100 indicates generally an apparatus for printing watermarkedimages in accordance with principles of the present invention. Theprinting apparatus 100 includes a postage meter 102. The postage meter102, in turn, includes a printer 104 and control circuitry 106 that iscoupled to, and controls operation of, the printer 104. (Althoughembodiments of the present invention are described herein in the contextof postage metering, those who are skilled in the art will recognizethat the methods of the invention may also be applied to production andverification of other types of secure documents, including papercurrency, travel and event tickets, and identification documents.) Theprinter 104 may be of a type that is capable of printing gray scaleimages or color images. For example, the printer 104 may include adye-sublimation printer. In some embodiments, the printer may be capableof printing 256 gray levels.

The printing apparatus 100 also includes a data center 108 that is incommunication with the control circuitry 106 of the postage meter 102via a data communication channel 110. The data center 108 may generate awatermarked image in accordance with the invention, and may download tothe postage meter 102 image data which represents the watermarked image.Using the downloaded image data, the postage meter 102 may print thewatermarked image as a part of postage meter indicia applied to mailpieces, which are not shown. Thus the mail pieces, and particularly thepostage meter indicia thereon, may constitute original documents which apostal authority may wish to verify.

FIG. 2 is a flow chart that illustrates a process performed inaccordance with the invention in the printing apparatus 100 of FIG. 1.

Initially, at step 200, an image is selected for watermarking. In someembodiments the image may be a standard image that is required to beprinted as part of every postage meter indicia by every postage meter,or by every postage meter that is part of a program for incorporating agray scale image in postage meter indicia. In other embodiments, theimage may be one of a number of standard indicia, any one of which maybe selected by the lessor of a postage meter as the image to beincorporated in indicia to be printed by the particular postage meter.In still other embodiments, the image may be a gray scale image that ischosen by the lessor of the postage meter from among images availablefor purchase or licensing, or may be generated by the lessor of thepostage meter. In these cases the selected image may be sent by thelessor of the postage meter to the data center for watermarking so thatthe image can be incorporated in indicia to be printed by the particularpostage meter. An image other than a gray scale image may alternativelybe used.

In some embodiments, the image to be watermarked may be represented bypixel data that represents, with respect to each pixel of the image, agray scale level. The number of available gray scale levels may be 256,in some embodiments. In such embodiments, each pixel may be representedby one 8-bit byte of image data, and the value of each pixel may be aninteger n, with n greater than or equal to zero and less than or equalto 255. Each value of n may correspond to a different gray scale level;in some embodiments the zero value corresponds to black, the value 255corresponds to white (no tone), and each value of n corresponds to atone which is darker than the tone which corresponds to n plus one.

Following step 200 is step 202. At step 202 a transformation may beapplied to the image data which corresponds to the image. Thetransformation may substantially approximate the effect on pixel valuesof first printing the image with the type of printer employed in thepostage meter, and then scanning the resulting image with a scanner ofthe type which is to be employed to verify the postage indicia. That is,the transformation applied at step 202 may be a print-scan distortiontransformation. FIG. 3 is a graph that illustrates an example of thetransformation that may be applied at step 202. In the graph of FIG. 3,the horizontal axis corresponds to pixel values prior to transformation,and the vertical axis corresponds to pixel values to which the priorvalues are mapped by the transformation.

The data illustrated in FIG. 3, or similar data for other printing andscanning equipment, may be generated according to the followingprocedure. First, image data may be generated that corresponds to astrip of gray scale blocks, each block corresponding to a respectivegray scale level, and the strip as a whole representing a sequence ofgray scale levels that spans the interval from white to black. A printedimage is then produced on the basis of the image data and using aprinter of the same type as the printer 104 of the postage meter 102(or, as the case may be, with a printer of the type with whichwatermarked images are to be printed). The printed image is then scannedwith a scanner of the type to be used in verifying or authenticating thewatermarked printed images, and the pixel values corresponding to eachgray scale block of the printed image are correlated with the gray scalevalues in original gray scale image data. With suitable interpolation,if appropriate, the correlation of the gray scale levels in the scannedimage data with the gray scale levels in the original image data may beused to generate a mapping such as that illustrated in FIG. 3.

As an alternative to the empirical mapping of gray scale values viaresults obtained from operation of a print-scan channel, other models ofthe print-scan channel may be devised. For example, the print-scanchannel may be modeled as a linear spatial filter, or as a non-linearspatial filter, and such a filter may be applied at step 202 to theimage data resulting from step 200.

Step 204 follows step 202 in FIG. 2. At step 204 a watermark is appliedto the image selected at step 200, as transformed at step 202. In someembodiments, the watermark applied at step 204 may be made by block-wiseadjustments in the tone (average gray scale level) in the transformedimage data, in a manner described in co-pending, commonly-assignedpatent application Ser. No. ______ Attorney docket no. F-713, which isfiled contemporaneously herewith and is entitled: “Fragile Watermark forDetecting Printed Image Copies”. This co-pending patent application ishereby incorporated herein by reference in its entirety.

Alternatively, another type of watermark may be applied at step 204. Forexample, the watermark applied at step 204 may be a phase-space encodedwatermark of the type described in co-pending, commonly-assigned patentapplication Ser. No. ______ Attorney docket no. F-714, which is filedcontemporaneously herewith and is entitled: “Detecting Printed ImageCopies Using Phase-Space Encoded Fragile Watermark”. This co-pendingpatent application is hereby incorporated herein by reference in itsentirety. Another type of watermark may alternatively be used, includingfor example any of a wide variety of conventional watermarks. As oneexample, there may be applied at step 204 the DFT-based watermarkdescribed in “Watermarking and Digital Signature Techniques forMultimedia Authentication and Copyright Protection” by Ching-Yung Lin(Ph.D. thesis submitted to Columbia University, 2000). In general, thewatermark applied at step 204 may be a “fragile” watermark, as describedin the above-referenced co-pending patent applications, or may be a“robust” watermark. Moreover, more than one watermark may be applied atstep 204, and the watermarks applied may include both a fragilewatermark and a robust watermark.

Both the original data that represents the image to be watermarked andthe watermark data itself may be gray scale data. Alternatively, one orboth of the original image data and the watermark data may include colorinformation, so that the resulting watermarked image may be at leastpartially in color.

Step 206 of FIG. 2 then follows. At step 206, the watermarked image issubjected to a transformation that is substantially or approximately theinverse of the print-scan distortion transformation that was applied atstep 202. Where the print-scan distortion transformation was in the formof a mapping of gray scales, the inverse transformation can be readilyderived from the forward direction transformation. FIG. 4 is a graphthat illustrates an example of the inverse transformation that may beapplied at step 206. In the graph of FIG. 4, the horizontal axiscorresponds to pixel values prior to the inverse transformation of step206, and the vertical axis corresponds to pixel values to which theprior values are mapped by the transformation.

If the print-scan distortion transformation that was applied at step 202took the form of a linear spatial filter, an inverse of that filter isapplied at step 206. Determining an inverse of a linear filter can bedone in a straight-forward manner and need not be described further. Ifthe print-scan distortion transformation that was applied at step 202took the form of a non-linear spatial filter, in some cases an inversefilter to be applied at step 206 can be readily derived from the forwarddirection filter; in other cases considerable experimentation may berequired to develop a satisfactory inverse direction filter thatsubstantially inverts the forward direction filter. It may be preferablenot to use at step 202 a nonlinear filter for which no inverse directionfilter can be derived. However, in alternatives to the embodimentsillustrated in FIGS. 5 and 8, it may not be necessary to provide aninverse transformation. For example, in the case of the embodiment ofFIG. 5, it may be possible to develop a map from post print-scan topre-print-scan gray scale levels by empirical experimentation.

With the completion of step 206, the watermarked image data is now incondition for use in printing images, and may be loaded into the postagemeter 102 (FIG. 1), as indicated at step 208 in FIG. 2. For example, thewatermarked image data may be downloaded from the data center 108 to thecontrol circuitry 106 of the postage meter 102 via the datacommunication channel 110. Alternatively, the image data may be copiedonto a floppy disk or other transportable data storage medium. Thestorage medium may then be mailed to the lessor of the postage meter andused to load the watermarked image data into the postage meter.

In any event, once the watermarked image data is present in the postagemeter 102, the control circuitry 106 may control the printer 104 toprint watermarked images (step 210, FIG. 2), based on theinverse-transformed watermarked image data, as part of postage meterindicia applied to mailpieces. In some embodiments, the image may beprinted at a resolution of 200 gray scale dots (pixels) per inch.

In accordance with conventional practices, the postage meter indicia mayinclude other information, including, e.g., postage amount, date,mailing location, postage meter serial number, two-dimensional barcode,etc. The data center may store data indicative of the watermark appliedat step 204.

FIG. 5 is a flow chart that illustrates a process that may be providedin accordance with an alternative embodiment of the invention forgenerating and printing watermarked images. The process illustrated inFIG. 5 may be particularly suitable in the case where a watermark to beapplied consists of data to be combined additively to the original imagedata, or in other cases in which application of the watermark isindependent of the content of the original image data. One example ofsuch an independently applicable watermark is the phase-space encodedwatermark described in the above-referenced co-pending patentapplication Ser. No. ______ Attorney docket no. F-714. The process ofFIG. 5 may, for example, be performed by a suitably programmed versionof the apparatus of FIG. 1.

Initially, at step 500 in FIG. 5, an image is selected for watermarking.This may be done in the same manner as described above in connectionwith step 200 in FIG. 2. Next, at step 502, there is provided and/orgenerated watermark data that represents the watermark to be combinedwith the selected image. Then, at step 504, a transformation is appliedto the watermark data that is available as a result of step 502. Thetransformation applied at step 504 is approximately or substantially theinverse of a print-scan distortion transformation that approximates thedistortion expected to result from printing the watermarked image andthen scanning the resulting printed image. Derivation of a suitableinverse transformation to be used in step 504 may be performed in thesame manner as was described above in connection with step 206 of FIG.2.

Following step 504 is step 506. At step 506, the inverse-transformedwatermark data resulting from step 504 is combined with original imagedata that represents the image selected at step 500. Step 506 mayinclude, for example, adding the original image data and theinverse-transformed watermark data. The result of step 506 iswatermarked digital image data that is ready for printing.

As indicated at step 508, the watermarked digital image data may beloaded into the postage meter 102. This may be done, for example, in anyof the ways described in connection with step 208 in FIG. 2. The postagemeter 102 may then be employed, as indicated at step 510, to printpostage meter indicia that include a printed image that represents thewatermarked image data produced at step 506.

FIG. 6 is a block diagram of an image examination apparatus 600 that maybe provided in accordance with the invention to examine printed imagesgenerated in accordance with the procedures of FIG. 2 or 5.

The image examination apparatus 600 may include a scanner 602 (e.g., a600 dpi scanner) to scan a substrate 604 (e.g., a mail piece) togenerate scanning image data that represents an image (not separatelyshown) carried on the substrate 604. The printed image scanned by thescanner 602 may be referred to as the “printed-image-under examination”or “PIUE”.

The image examination apparatus 600 further includes a processor 606that is coupled to the scanner 602. The processor 606 may processscanned image data generated by the scanner 602, and may store scannedimage data in a memory 608 that is coupled to the processor 604. Thememory 608 may serve as a program store and as working memory, as wellas a scanned image data store.

The image examination apparatus 600 may further include a user interface610 which is coupled to the processor 606 to allow an operator of theapparatus to provide input to the processor and to receive output fromthe processor. In addition, the processor 606 may be temporarily orpermanently coupled to a data center (which may be the data center 108of FIG. 1) via a data communication channel 612.

FIG. 7 is a flow chart that illustrates a process that may be performedin accordance with the invention by the image examination apparatus 600of FIG. 6 to examine a PIUE.

According to a first step 700 in the process of FIG. 7, the apparatus600 scans the PIUE via the scanner 602 to generate scanned image data.The scanned image data is made up of pixel data that may be constitutedby gray scale values and represents the PIUE as a set of scanningpixels. The scanned image data may be pre-processed by the processor 606and/or stored in the memory 608.

Next is step 702, at which the processor 606 analyzes the scanned imagedata produced at step 700 to retrieve the watermark that wasincorporated in the PIUE and/or to determine a characteristic of thewatermark as it passed through the print-scan channel. For example, insome embodiments, if the watermark was a “fragile” watermark, acharacteristic of the watermark as retrieved from the scanned image datamay be compared with a characteristic of the original watermark datathat was combined with the original (or forward direction transformed)image data. If the watermark as retrieved from the scanned image datadiffers by less than a threshold amount from the original watermarkdata, then the apparatus 600 may determine that the PIUE is an originaldocument (e.g., a legitimate postage meter indicia). If the watermark asretrieved from the scanned image data differs from the originalwatermark data by more than the threshold amount, then the apparatus 600may determine that the PIUE is a copy of an original document (e.g., afraudulent copy of a postage meter indicia).

The present inventor has found that the compensation for print-scanchannel distortion that may be provided by the present invention mayenhance the detectable differences between a fragile watermark in anoriginal document and the fragile watermark as reproduced in a copy ofan original document.

In one experiment, the above-referenced tonal fragile watermark(described in above-referenced co-pending patent application Ser. No.______ Attorney docket no. F-713) was applied to image data after theimage data was transformed in accordance with a print-scan distortiontransformation. The resulting transformed image data was thenwatermarked with the tonal watermark and the watermarked image data wasthen subjected to a second transformation that was substantially theinverse of the print scan distortion transformation. The inversetransformed watermarked image data was used to print an original imagewith a resolution of 200 dpi. The original image was scanned at 600 dpiand the tonal watermark was retrieved from the scanned image data todetermine a metric indicative of the difference between the watermark asretrieved from the scanned image data and the watermark as originallyapplied to the forward direction transformed original image data. Inthis case the print-scan transformation mapping was derived empiricallyby transmitting a strip of gray scale blocks through the print-scanchannel.

The original printed image was also scanned at 1200 dpi to producesecond scanned image data, and a copy of the original printed image wascreated by printing at 1200 dpi from the second scanned image data tosimulate a high-quality copying attack on the original printed image.The copy printed image was then scanned at 600 dpi and subjected to thesame watermark detection procedure to generate the metric with respectto the copy printed image to indicate the difference between thewatermark as retrieved from the scanned copy image and the watermark asoriginally applied to the forward direction transformed original imagedata.

In a control procedure, the forward direction and inverse transformationsteps were omitted and the corresponding metrics were obtained for theresulting original and copy printed images. The difference between therespective metrics for the original and the copy was considerably lessin the control procedure than when the forward direction and inversetransformation steps were used. Thus the inverse transformation may haveenhanced the ability of the procedure to distinguish between originaldocuments and copies by pre-compensating for distortion to the watermarkdata caused by transmission through the print-scan channel.

In some embodiments, if the watermark is applicable to the image dataindependently of the content of the image data, the process of FIG. 2may be modified by dropping step 202. Alternatively, as noted above, theprocess of FIG. 5 may be employed.

FIG. 8 is a flow chart that illustrates a process that may be providedin accordance with another alternative embodiment of the invention.Initially in FIG. 8, as indicated by step 800, an image to bewatermarked is selected. This may be done in the same manner asdescribed above in connection with step 200 of FIG. 2. Next, asindicated in step 802 of FIG. 8, a watermark is applied to image datathat represents the selected image. Then, at step 804, a print-scandistortion transformation is applied to the watermarked image dataproduced at step 802. At step 806, the transformed watermarked imagedata produced at step 804 is analyzed to retrieve a characteristic ofthe watermark as represented by the transformed watermarked image data.Data indicative of the retrieved characteristic may be stored for futurereference.

As indicated in step 808, an original printed image may be generated byusing the watermarked image data produced at step 802 (i.e., the printedimage is produced by the image data as it existed prior to print-scandistortion transformation). Then, at step 810, the original image (or aPIUE not known to be original) may be scanned to produce scanned imagedata. At 812, the scanned image data produced at step 810 is analyzed toretrieve a characteristic of the watermark as represented by the scannedimage data. As indicated by step 814, the results of steps 806 and 812may be compared to, e.g., authenticate the image scanned at step 810.

The process of FIG. 8 may be particularly helpful in the case of aprint-scan distortion transformation model for which the inversetransformation is computationally intensive or for which no inversetransformation can be derived. The process of FIG. 8 may, for example,be performed using suitably programmed versions of the apparatus ofFIGS. 1 and 6.

In another application of the print-scan or inverse print-scantransformations described herein, it may be possible to analyze aprinted image to determine whether the image was printed or scanned witha printer or scanner other than an expected or standard printer orscanner.

The words “comprise,” “comprises,” “comprising,” “include,” “including,”and “includes” when used in this specification and in the followingclaims are intended to specify the presence of stated features,elements, integers, components, or steps, but they do not preclude thepresence or addition of one or more other features, elements, integers,components, steps, or groups thereof.

A number of embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Thepresent invention may be applied, for example, to verification ofdocuments other than postage indicia. Other variations relating toimplementation of the functions described herein can also beimplemented. Accordingly, other embodiments are within the scope of thefollowing claims.

1. A method comprising: providing digital image data that represents animage; applying a digital watermark to the digital image data to producewatermarked digital image data; and applying a transformation to thewatermarked digital image data to produce transformed watermarkeddigital image data, the transformation being at least approximately aninverse of a print-scan distortion transformation.
 2. The methodaccording to claim 1, further comprising: applying the print-scandistortion transformation to the digital image data prior to the step ofapplying the digital watermark to the digital image data.
 3. The methodaccording to claim 2, further comprising: printing an image on the basisof the transformed watermarked digital image data.
 4. The methodaccording to claim 3, further comprising: scanning the printed image toproduce scanned image data.
 5. The method according to claim 4, furthercomprising: analyzing the scanned image data to retrieve the watermarktherein.
 6. The method according to claim 1, further comprising: loadingthe transformed watermarked digital image data into a postage meter. 7.The method according to claim 6, further comprising: using the postagemeter to print a postage meter indicia on a mail piece, the postagemeter indicia including a printed image based on the transformedwatermarked digital image data.
 8. The method according to claim 7,further comprising: scanning the printed image to produce scanned imagedata.
 9. The method according to claim 8, further comprising: analyzingthe scanned image data to retrieve the watermark therein.
 10. The methodaccording to claim 2, further comprising: applying the print-scandistortion transformation to the digital image data prior to the step ofapplying the digital watermark to the digital image data.
 11. A methodcomprising: providing watermark data that represents a digitalwatermark; applying a transformation to the watermark data to producetransformed watermark data, the transformation being at leastapproximately an inverse of a print-scan distortion transformation;providing digital image data that represents an image; and combining thetransformed watermark data with the digital image data to producewatermarked digital image data.
 12. The method according to claim 11,further comprising: printing an image on the basis of the watermarkeddigital image data.
 13. The method according to claim 12, furthercomprising: scanning the printed image to produce scanned image data.14. The method according to claim 13, further comprising: analyzing thescanned image data to retrieve the watermark therein.
 15. The methodaccording to claim 11, further comprising: loading the watermarkeddigital image data into a postage meter.
 16. The method according toclaim 15, further comprising: using the postage meter to print a postageindicia on a mail piece, the postage meter indicia including a printedimage based on the watermarked digital image data.
 17. The methodaccording to claim 16, further comprising: scanning the printed image toproduce scanned image data.
 18. The method according to claim 17,further comprising: analyzing the scanned image data to retrieve thewatermark therein.
 19. A method comprising: (a) providing digital imagedata that represents an image; (b) applying a digital watermark to thedigital image data to produce watermarked digital image data; (c)applying a print-scan distortion transformation to the watermarkeddigital image data to produce transformed watermarked digital imagedata; (d) retrieving a characteristic of the watermark as represented bythe transformed watermarked digital image data produced at step (c); (e)printing an image on the basis of the watermarked digital image dataproduced at step (b); (f) scanning the printed image to produce scannedimage data; (g) retrieving a characteristic of the watermark asrepresented by the scanned image data produced at step (f); and (h)comparing the characteristic retrieved at step (d) with thecharacteristic retrieved at step (g).